The present invention relates to magnetic transducer assemblies, and more particularly to the surface configuration of magnetic heads adapted to read or write information upon a passing magnetic tape.
The principle of placing information upon a moving magnetizable surface, and subsequently deriving the information therefrom, has been utilized for many years in various types of apparatus. Paramount among these is the computer, which makes use of magnetizable tape for storing and recording information in digital form. Typically, the recorded signals take the form of small areas of tape surface, the microscopic magnetic domains of which have been reoriented to form a magnetized area of one of two polarities. As the tape is transported by a reading mechanism these areas are sensed and a digital "1" or "0" is inferred. By appropriately combining the digital signals in a manner now well known to those skilled in the art vast amounts of information can be stored in a relatively small volume.
In order to derive blocks of digital information from a length of magnetic tape, a tape transport apparatus is required to accelerate the tape to a working velocity, transport the tape past an appropriate read or write transducer, and then bring the tape to a halt. Since the area of tape required for blocks of information may be relatively small, it will be appreciated that relatively high rates of acceleration and deceleration are needed in order to keep the unused area of tape to a minimum. Thus, it is highly desirable to be able to accelerate the magnetic tape medium to a working velocity as quickly as possible. Further, since it is often desired to read or write signals in the reverse direction, the system must also have the capability of accelerating the tape in the reverse as well as the forward direction.
One problem which has plagued prior art tape transport systems, particularly those in which the rate of acceleration of the transported tape was relatively high, is a temporary instability in tape position which arises upon reverse acceleration thereof. It has long been recognized that in rapidly transporting a length of foil, such as magnetic tape, over a bearing surface a hydrodynamic effect occurs wherein a thin layer of air forms between the tape and the bearing surface. The thickness of this gap, or layer of air, varies with tape speed and bearing surface characteristics. In order to take advantage of this effect, attempts are commonly made to provide a tape drive head with a surface or bearing configuration which supports a consistent gap between the tape and the head surface.
While this desideratum has been achieved in varying degrees in prior art systems, the theory which explains both steady-state and transient characteristics of the hydrodynamic bearing is neither fully developed nor completely understood. The contours of many head designs, while performing acceptably under many conditions, nonetheless support a transient instability when te transported tape is accelerated in a reverse direction. While the specifics of the phenomenon are not completely understood it appears that, at least with some head configurations, the tape bulges away from the head surface at some point while undergoing acceleration in the reverse direction. In a single capstan drive system wherein a capstan in effect "pushes" the tape across the head during reverse drive mode, a temporary lessening of tape tension occurs during the reverse acceleration period. The lessened tension and the drag forces acting on the tape give rise to a momentary outward bulging of the tape surface, away from the head surface. In cases where the aforementioned bulge occurs adjacent the reading or writing transducer an increased separation occurs between the tape and the transducer surface. The separation then continues until the system stabilizes, usually some time after the desired terminal velocity of the tape is achieved.
Since information is transferred to and from the magnetizable areas on the tape by means of inductive coupling with ones of the transducers in the head, the proximity of the tape to the head is critical. It will be understood that, as the separation between the tape and heads increases a severe lessening of the lines of magnetic flux linking the transducer and tape areas occurs with an accompanying probability that information will be incompletely transferred between head and tape. Should the separation become great enough, no information will be transmitted to or from the tape and the information comprising the initial portions of the block of information to be transmitted will be lost.
With the advent of improved tape compositions capable of being magnetized in smaller areas, and therefore of encoding information in a much higher density than previously, the criticality of coupling between the tape and tranducers is increased still further. Transient separations occurring at the beginning of a block of information, and which may have been tolerated in the past, can be sufficient to vitiate the entire block where densely packed information is present on the tape. For all of the foregoing reasons, it should be understood that it would be highly desirable to provide a tape transducer head assembly having a contour which does not support transient increases in tape-to-head gap during accelerative intervals of tape transport.
It is therefore an object of the present invention to provide a transducer head for interacting with magnetic tape which produces only insignificant, if any, increased separation during tape reverse acceleration.
It is another object of the invention to provide a method for forming the bearing surfaces of an improved magnetic tape transducer which will substantially preclude undue separation between the tape and transducer surface during reverse acceleration of the tape.